It is the purpose of the proposed project to facilitate the induction of permanent specific organ transplant survival in the dog, on the basis of further study of the immunogenetic components of the main histocompatibility system in the canine species. In vitro serological techniques capable of detecting the corresponding alleles of the canine main histocompatibility system (SD alleles) of the DL-A system, as well as mixed leucocyte culture techniques, and cell lympholysis studies will be performed for this purpose in the selectively bred lines of dogs maintained at the Cooperstown Colony for the past 12 years of research. It is hoped that information gained in the course of such studies will be applied peri pasu to attempts to induce tolerance to organ transplants in mongrel dogs as well, through the utilization of total body irradiation and bone marrow transplantation under controlled conditions of donor-recipient genetic histocompatibility.